The focus of modern network communications is directed to delivering services, such as broadcast video, Plain Old Telephone Service (POTS), Voice over Internet Protocol (VoIP), video on demand, and Internet access, and deploying these services over an Ethernet-based network. In recent years, the types of services provided, their quality and sophisticated implementation, have all been improving at a steady pace. In terms of providing uninterrupted network operations and fast responses to network link failures, however, today's Ethernet-based network communications are falling behind. Some additional shortcomings of existing Ethernet-based networks include unreliable self-recovery from multiple link failures, and inability to make the failures and the recovery transparent to the subscriber.
Existing network protocols, such as the Spanning Tree Protocol (“STP”), initially specified in ANSI/IEEE Standard 802.1D, 1998 Edition, and the Rapid Spanning Tree Protocol (“RSTP”), defined in IEEE Standard 802.1w-2001, are effective for loop-prevention and assuring availability of backup paths, and are incorporated by reference herein in their entirety. Although these protocols provide the possibility of disabling redundant paths in a network to avoid loops, and automatically re-enabling them when necessary to maintain connectivity in the event of a network failure, both protocols are slow in responding to and recovering from network failures. The response time of STP/RSTP to network failures is up to 30 seconds. This slow response to failures is due, in part, to the basics of STP/RSSTP operations, which are tied to calculating the locations of link breakage points on the basis of user-provided values that are compared to determine the best (or lowest cost) paths for data traffic.
Another existing network algorithm and protocol, Ethernet Protected Switched Ring (“EPSR”), developed by Allied Telesis Holdings Kabushiki Kaisha of North Carolina on the basis of Internet standards-related specification Request for Comments (“RFC”) 3619, is a ring protocol that uses a fault detection scheme to alert the network that a failure has occurred, and indicates to the network to take action, rather than perform path/cost calculations. The EPSR, however, although much faster to recover from a single link failure than STP/RSTP, suffers from the drawback that recovery from multiple link failures is not possible, and traffic on the network cannot be restored (interchangeably referred to herein as “converged”), until recovery of all failed links. Moreover, self-recovery from multiple link failures is unreliable, and even if ultimately accomplished, is cumbersome and slow.
There is a general need, therefore, for methods and systems that provide network recovery from multiple link failure conditions. There is a further need for methods and systems that provide network recovery from multiple link failure conditions that are fast, provide reliable self-recovery from failures, and make the failures and the recovery unnoticeable to the subscriber, while preventing the forming of network loops.